Conventionally, when a liquid crystal display element is manufactured, a cell gap in the liquid crystal display element (thickness of a liquid crystal layer) has been controlled by carrying out the following process after combining a pair of electrode substrates. A pair of electrode substrates are first combined, using a spacer and a thermosetting type sealing material as a sealing material therebetween, and then a plurality of combined pairs of electrode substrates are stacked. The electrode substrates are pressed with a pressing machine and heated at the same time.
However, since the electrode substrates are mechanically pressed by the pressing machine, the following problems inevitably occur with the method: It is difficult to uniformly press the whole electrode substrates even if upper and lower pressing plates provided to the pressing machine are highly parallel and have a smooth surface, and the combined electrode substrates have smooth surfaces. In addition, since a plurality of pairs of electrode substrates are stacked when pressed, if one of the pairs is irregularly pressed, the irregularity in pressing accumulates, possibly affecting the uniformity of the cell gap. Moreover, if there is a foreign substance on the electrode substrate, an extra heavy load is created locally, which makes irregular display coloring more likely to happen.
Japanese Laid-Open Patent Application No. 4-291320/1992 (Tokukaihei 4-291320) and Japanese Laid-Open Patent Application No. 6-175097/1994 (Tokukaihei 6-175097) are disclosure examples regarding methods to solve these problems of irregularity in pressing, affection from a foreign substance, etc.
Japanese Laid-Open Patent Application No. 4-291320/1992 (Tokukaihei 4-291320) discloses a method of putting a combined pair of electrode substrates in a wrapping bag and evacuating the air in the wrapping bag for depressurization thereof. In other words, the method creates a closed space containing the electrode substrates and utilizes a difference between atmospheric pressure and a pressure in the wrapping bag for pressing. According to this conventional method, after the air in the wrapping bag is evacuated for depressurization thereof, an exhaust port is closed, and then a thermosetting type sealing material is cured by heating. The pressure is specified to 20 to 1.2 Torr after evacuation to prevent the sealing material to bubble and sealing edge to become irregular.
Meanwhile, Japanese Laid-Open Patent Application No. 6-175097/1994 (Tokukaihei 6-175097) , similarly to the above disclosure example, discloses a method of evacuating a space between a combined pair of electrode substrates in a closed space for depressurization thereof and thereby utilizing a difference between atmospheric pressure and an internal pressure for pressing.
According to this method, the whole electrode substrates are uniformly pressed. Besides, since the electrode substrates and a sealing material are adhered under vacuum atmosphere, the air is prevented from remaining on adhesion surfaces of the electrode substrates and the sealing material.
However, according to the method disclosed in Japanese Laid-Open Patent Application No. 4-291320/1992 (Tokukaihei 4-291320), the pressing utilizing the difference between atmospheric pressure and the pressure in the wrapping bag and the curing of the sealing material with heat are conducted separately. As a result, this method entails difficulty in forming a good sealing portion, i.e., difficulty in preventing the sealing edge to become irregular. Moreover, a foreign substance in the wrapping bag results in an irregular pressing, which in turn causes the irregular display coloring to be more likely to happen.
Furthermore, according to the method disclosed in Japanese Laid-Open Patent Application No. 6-175097/1994 (Tokukaihei 6-175097), the air in a portion composing the liquid crystal display element between the pair of electrode substrates is evacuated only through an exhaust port portion of the liquid crystal display element. Therefore, at an early stage of the evacuation, since there occurs a great difference in pressure between a portion composing the liquid crystal display element and a portion not composing the liquid crystal display element between the electrode substrates, the sealing material itself bubbles and the sealing edge is more likely to become irregular. In addition, at an early stage of the evacuation, since the air flows fast near the exhaust port portion, the spacer in the portion composing the liquid crystal display element moves easily and thus makes the irregular display coloring more likely to occur.